This invention relates to protective coatings for use in high temperature environments. More particularly, this invention relates to methods for manufacturing coated articles for use in high-temperature environments. This invention also relates to articles for use in such environments.
Materials used in high-temperature applications such as, for example, gas turbine engines, heat exchangers, internal combustion engines, and the like, are typically subjected to a potentially detrimental combination of heat, oxidative gas mixtures (including air, for instance), and other deleterious species such as water vapor. Protective coatings are often applied to component surfaces to prolong service lives and enhance performance. Thermal barrier coatings (TBC's) and environmental barrier coatings (EBC's) are two examples of protective coatings used in these and other applications. TBC's often comprise a layer of material, such as, for example, yttria-stabilized zirconia, having low thermal conductivity and high resistance to hot gas. EBC's are often used where the operating environment of a machine is corrosive or otherwise chemically detrimental to the materials comprising the bulk of key components. For example, U.S. Pat. No. 6,387,456 describes a method for applying an EBC to silicon based substrate materials, which have been proposed for use in high temperature applications. The EBC in this work comprised a barium-strontium aluminosilicate (BSAS) barrier layer, which protects the silicon-bearing substrate from environments containing high-temperature water vapor. Intermediate layers are also often applied between the substrate and EBC or TBC to provide enhanced adhesion, oxidation resistance, thermal expansion match, and the like.
EBC's and TBC's, which are generally ceramic materials, are often applied using thermal spray methods, including, for example, air plasma spraying, vacuum plasma spraying, and high velocity oxy-fuel (HVOF) spraying. The application of a high-performance, protective EBC or TBC presents a significant technical challenge, because the microstructure and properties of the finished coatings depend in large part on the process parameters used during the thermal spray application of the coating material. Such coatings are often required to possess a balance of competing properties such as, for example, high density and high tolerance for strain. Selection and control of thermal spray process parameters is thus an important aspect of the manufacture and repair of articles for use in high-temperature applications.
Therefore, there is a need to provide methods to control the microstructure and properties of protective thermal sprayed coatings, in order to improve the service lives and performance of high-temperature components. There is a further need for articles having enhanced performance in high-temperature applications.